The invention relates to an electromagnetically activated pump of the type finding particular application in the metered supply of fuel to burner devices, as for instance, to burners in fuel operated heating appliances.
German Offenlegungsschrift, No. 23 15 842 and U.S. Pat. No. 202,582 disclose electromagnetically activated piston fuel pumps particularly adapted for fuel burners, and German Patent No. 23 66 301 discloses a similar pump arrangement wherein the inlet and outlet are axially arranged across from each other. Pump activation is based on pulse frequency of a current supplied to a magnetic coil assembly, which frequency effects the stroke of the piston. A return spring returns the piston in the opposite direction. During its stroke, the piston expels the fuel at the outlet via a self-opening pressure valve, while simultaneously opening a valve at the inlet so that fluid medium, i.e., the medium being pumped, such as fuel, enters the piston pump and flows along the outside of the piston in an axial direction. At the end of the delivery stroke, the piston reverses its direction of movement and the flow medium is displaced, during a working stroke in the pump, to a cylindrical chamber, the fluid medium entering from an armature compartment formed between the armature and the magnetic coil assembly, shortly before completion of the piston return movement. After completion of the piston return movement, the valve at the inlet is closed during the working stroke.
In this piston pump, the valve at the inlet may open itself in the inactive position of the piston, e.g., when the piston pump is turned off, as a function of the supply pressure, thereby permitting the fluid medium to enter the pump in a manner causing pressure to be applied to the self-opening pressure valve with the result that there is no longer a complete closure of the pump outlet. Furthermore, the ability of the valve at the inlet to completely close depends only upon the spring force exerted by the return spring, which can be overcome when there is corresponding supply pressure.
Another drawback of such pumps is that when the fluid medium is gasoline, a considerable out-gassing takes place within such pumps, which is even more intensified as the fluid medium is displaced by way of grooves in the pump which have converging flow-through cross-sectional areas, and inasmuch as the fluid medium enters the cylindrical chamber during displacement, only at the end of the working stroke movement, which movement is counter to the return movement of the piston. Consequently, during this working stroke, negative pressure is created for intake into in the inlet zone, which promotes out-gassing of the fuel, and inherently promotes formation of vapor bubbles. The formation of such vapor bubbles in the piston pump results in an uneven flow supply at the outlet of the piston pump which, in turn, can lead to operating disturbances in the burner devices.
It is, therefore, a primary object of the invention to overcome the above described drawbacks and problems and to provide an electromagnetically activated piston pump which delivers a uniform flow substantially free of bubbles, and permits a reliable complete closure.
In accordance with the invention, the design of the electromagnetically activated piston pump is such that, at the inlet of the piston pump, there is a suction valve leading to a suction chamber, which valve is opened by pressure a differential acting on the suction valve. Furthermore, the piston, energized by the magnetic coil assembly, executes a working stroke for displacement of the fluid medium from the suction chamber, via a relief valve, to the armature compartment. During the return movement of the piston for executing the delivery stroke, the fluid medium is expelled from the armature compartment to the outlet, with the relief valve in a blocked position. Immediately at the outset of this counter-current movement of the piston, the suction valve opens and the suction chamber is again filled with fluid medium.
As, moreover, the suction chamber can again fill with fluid medium via the suction valve at the beginning of the return movement of the plunger for the execution of the delivery stroke, the fluid medium is introduced into the suction chamber with as low a negative pressure as possible, in order to avoid bubble formation. Furthermore, the inventive design is such that there is complete closure in the area of the pump outlet in order to make sure that, particularly in this basic or inactive position of the plunger pump, no fluid medium is delivered, thereby assuring operational safety of the burners supplied by such piston pumps.
Even if the fluid medium should enter at the inlet of the piston pump of the present invention, the valve producing the outlet closure is acted upon in a closing direction by any flow medium which might enter, via the piston and armature, causing an even tighter sealing thereof. This also has the advantage that the complete closure at the outlet is intensified by the fluid medium itself, if there is excessive supply pressure, ensuring tight sealing of the outlet in the idle position. As the armature compartment and the suction chamber are separated by the relief valve, the metered volume of the fluid medium, determined by the suction chamber, cannot change, even if there is a possible formation of vapor bubbles caused by either the displacement action, or by heating of the armature compartment.
The preferred arrangement of the suction valve, with regard to the piston, and particularly to its work stroke limiting positions, permits an extremely advantageous construction of the housing arrangement, making the utmost use of the specified available installation space, while ensuring reliable performance of their functions on a long term basis.
In order to extensively reduce the supply pressure dependency of the piston pump, the outlet of the suction valve, preferably at the end of the working stroke displacement, is overlapped by the piston itself, so that this outlet is blocked off by the position of the piston, without additional measures. In order to avoid having to resort to additional measures for a forced opening of the relief valve in the area of the working stroke limiting position of the piston, the inactive flow volume in the area of the suction valve is reduced, in that the suction valve is a poppet value, and in that the value seat is disposed at the discharge area of the suction chamber. The poppet valve is biased into its closed position by a spring.
Preferably, resilient stops are provided for the stroke limiting positions of the piston for the purpose of noise reduction.
The spring biased relief valve, preferably, may be a ball valve, a conical seat valve, or, especially, a needle valve which has the advantage that the inactive flow volume in the area of the relief valve may be kept to a minimum.
According to one modification in accordance with the invention, the relief valve is arranged in a cylindrical housing, which design simplifies the manufacture of the piston as one solid component, thereby simplifying the manufacture and attachment of the armature, and finally permitting the relief valve and the suction valve to be disposed at areas easily accessible from the exterior of the piston pump where, therefore, if necessary, they can be easily exchanged or repaired. Additionally, a transit channel can easily be provided in the housing of the pump, which creates a connection between the outlet of the relief valve and the armature compartment. Appropriately, this transit channel is formed by a minimum of one through-bore in the cylindrical housing, which extends parallel to the piston axis.
In a preferred embodiment of the invention, the suction valve is disposed extending axially to the piston, and the relief valve is disposed in the housing so as to be perpendicularly oriented and laterally situated relative to the suction valve. The inlet to the relief valve is in the side of the suction chamber. As the piston approaches the end of its fuel delivery stroke, the piston increasingly overlaps the inlet leading to the relief valve, so that the cross-sectional area of the inlet opening is reduced and the moving speed of the piston can be reduced, resulting in a lower impact speed of the piston at the stop. At the same time, such a design enables the valve head of the suction valve to serve as a stroke limiting device, thereby combining two functions in the valve head and further creating a minimum of inactive flow volume.
If, according to an alternative embodiment of the invention, the relief valve is arranged in the housing so as to be oriented in the axial direction of the piston, and the suction valve is oriented normal thereto, i.e., pointing to the side, if necessary a forced opening of the relief valve, at the stroke end of the piston working stroke, can easily be realized, if there is design-conditioned unavoidable inactive flow volume. This forced opening can be achieved by having an extension of the valve nose project into the suction chamber, so that the piston will open the relief valve by contacting the extended valve nose before the plunger reaches the end of its stroke.
When the relief valve is arranged at the side of the housing, the transit channel to the armature compartment can easily be provided by a constructional design which leaves an annular clearance free for forming an annulus between two housing parts, whereby the suction valve is arranged in one housing part, and the relief valve is disposed in a second housing part, complementary thereto.
According to a further embodiment of the invention, the arrangement is such that at least a portion of the piston, and, preferably, the inlet end of the piston facing the suction valve, comprises a hollow space which serves to displace the flow medium from the suction chamber to the armature compartment and contains the relief valve. In such a design, a short valve element with a small inertial mass can be used for reducing the opening pressure. Simultaneously, a constructionally simple design of the housing is achieved since, in such an embodiment, the displacement of the fluid medium to the armature compartment occurs via the hollow space in the piston so that no transit channels or connections from the suction chamber to the armature compartment have to be provided through the housing. Such a design further makes it unnecessary for the housing to contain the relief valve. In order to keep the inactive flow volume to a minimum, which otherwise could present difficulties with respect to gas delivery, a needle type relief valve is arranged with its valve seat in the vicinity of the front area of the inlet end of the piston.
When such design is adopted, particularly when the suction valve is in the form of a poppet valve, the inactive flow volume obtained is negligible with regard to the functioning of the pump in connection with the gas delivery, so that no additional measures have to be taken to ensure a forced opening of the relief valve immediately at the end of the working stroke of the piston pump. As such a design provides that the fluid medium is guided through the hollow space of the piston during displacement, out-gassing of the fluid medium during displacement can be prevented, or extensively be kept to a minimum.
A particularly uncomplicated construction of a piston having a hollow space is obtained when that part of the piston facing the outlet is a solid component, provided with a step-like extension, onto which a casing is placed for the formation of the hollow space. Such a design also offers the advantage that the valve needle of the needle valve can be secured in a spring, which biases it into a closed position, between the needle element and the reduced diameter section of the solid piston, and that the needle valve structure can be simply inserted during the assembly of the casing and solid piston part. Further, the channel leading to the armature compartment may be designed as bores in the casing.
An alternative piston pump embodiment, in accordance with the invention, is characterized in that the entire piston is hollow. In such design, the relief valve is appropriately disposed in the inner chamber formed by the hollow piston, in the vicinity of the outlet side end thereof. The armature can be rigidly connected with the hollow piston and there may be several connecting channels therein which create a connection to the armature compartment during displacement.
In such an arrangement, however, there is a relatively large inactive flow volume formed by the inner cavity of the hollow piston so that a forced opening of the relief valve at the end of the piston working stroke is necessary to preclude difficulties in connection with the conveyance of gas. To this end, an activating element which contacts the relief valve is arranged in the hollow space of the hollow piston in such a manner that it opens the relief valve at the end of the piston working stroke as a consequence of the activating element engaging against the front facing side of the pump inlet, thereby forcing the valve element of the relief valve into its open position.
In a coaxial arrangement of the inlet and outlet of the piston, in order to suppress the supply pressure dependency of such a piston pump, the outlet of the suction valve, at the end of the working stroke, is overlapped by the hollow piston itself so that, during the forced opening of the relief valve caused by the actuating element, discharging from the inlet into the suction chamber is reliably blocked.
Appropriately, the actuating element, particularly at the end facing the inlet valve, is disposed such that it forms a seal for blocking the outlet at the end of the working stroke. This causes the actuating element to simultaneously perform the function of a valve element for blocking the outlet of the suction valve during the forced valve opening of the relief valve, ensuring independence from supply pressure. This seal provided at the end of the suction valve facing the outlet is pressed against the outlet of the suction valve during the forced valve opening.
In a further refinement of this design, the valve seat of the relief valve is directly disposed at the end of the outlet side of the hollow piston, and the valve element is provided on the actuating member. Such an arrangement simplifies the construction and the design of the relief valve, having a forced opening part, as the actuating element simultaneously is disposed and functions as a valve element at its end that faces away from the inlet.
In order to achieve a stroke synchronization for the piston of the pump in a simple manner, a design provision for an axially adjustable outlet connection is applicable for all forms of the piston pumps, and can, for instance, be positioned in the area of the outlet by way of a retaining nut, at a predetermined axial point.
Finally, means may be provided for preventing fluctuations in the flow volume, to be displaced by the piston, which fluctuations might occur in connection with the expansion of the resilient stops at the end positions of the piston. To this end, in order to obtain a flow volume that is as uniform as possible, a bypass channel is provided that terminates at the inlet to the suction chamber, at an axial distance from the outlet of the suction valve, and which communicates with the inlet line upstream of the suction valve. In this case, the volume of fluid medium to be conveyed to the armature compartment is not determined by the end position of the piston. Instead, the volume displaced at the piston pump is predetermined by the axial distance of the bypass channel discharge opening into the suction chamber from the inlet, permitting a predetermined volume to be displaced in the piston pump, independent of any expansion of the resilient stop at the end of the working stroke. This particularly eliminates the flow fluctuations which are the result of temperature changes of the piston pump and/or of expansion of the resilient stops in the end positions of the piston displacement.
At the outset of the discharge process, the flow medium is returned upstream again to the inlet line via the bypass channel process, until the piston travels over the discharge opening of the bypass channel in the suction chamber. At that point, flow medium is then fed downstream so that the flow volume that is displaced corresponds to the volume which is contained between the front wall of the suction chamber and the piston at the point where the piston seals the bypass channel outlet. The selection of the axial distance at the outlet opening of the bypass channel into the suction chamber from the front wall of the suction chamber permits the displacement volume, and thereby the flow quantity delivered by the plunger pump, to be varied and adjusted. When also the relief valve opens into the suction chamber, the flow volume is extensively independent of the expansion effects of the two resilient stops, so that the displacement volume and the respective flow quantity are determined by that volume which is confined between the discharge opening of the bypass channel and the inlet opening of the relief valve in the suction chamber. The flow volume in the suction chamber is determined by control edges rather than the end positions of the piston.
If no displacement is desired, the relief valve can be an outlet valve, like a pressure valve. As a result the advantages, previously discussed, are obtained, relative to flow delivery by the outlet valve.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.